Approximately half of Mexican-American women report having a sedentary lifestyle, and nearly 78 percent are overweight or obese. Compared to women in all other ethnic groups, Mexican-American women have the highest lifetime risk of type 2 diabetes. The development of culturally appropriate lifestyle interventions for this population is an urgent priority, and the proposed study accordingly will investigate a novel dyadic intervention designed to improve health behaviors and promote weight loss in two at-risk members of the same family: mothers with type 2 diabetes and their overweight/obese adult daughters who are at risk for developing diabetes. The intervention, Unidas por la Vida (United for Life), capitalizes on the importance of the family in Latino culture to mobilize an existing family dyad as a source of mutual support that is likely to foster greater and longer-lasting healt behavior change. The study builds on a successful pilot study (R34 DK083500) that established the feasibility and acceptability of this dyadic behavioral lifestyle intervention in a high-risk sample of Mexican-American family members who share a risk for diabetes and its complications. The 16-week intervention was modeled after the Diabetes Prevention Program (DPP), but was adapted for use with mother- daughter pairs and to be community-based and, thus, more easily accessible to low-income Latinas. Preliminary data from the Unidas pilot study indicated that the dyadic intervention promoted significant weight loss. The proposed study extends the successful pilot study to: 1) target weight loss > 5 percent of baseline body weight and to foster maintenance using a tapered intervention, 2) add comparison groups that permit evaluation of the improvement uniquely associated with the partner intervention, and 3) assess theoretically derived mediators of the intervention. Participants (N=460 mother-adult daughter dyads) will be randomized into one of three conditions: 1) dyadic (mother-daughter) participation in a Unidas partner intervention (Arm 1); 2) individual participation (mothers alone; unrelated daughters alone) in a Unidas individual intervention (Arm 2); and 3) mother-daughter dyad in a usual care only condition (Arm 3). The primary outcome is weight loss. Secondary outcomes include physical activity, dietary intake, physiological measures (e.g. HbA1c, LDL), body composition, quality of life, cost, and process evaluation. It is hypothesized that both the partne and individual interventions will produce significantly greater weight loss at 6, 12, and 18 months following program initiation than will the usual care only condition, with women assigned to the partner intervention losing more weight and maintaining the weight loss longer than women assigned to the individual intervention.